Highlights d ARfl and ARv7 genomic binding is interdependent and colocalized d ARv7, unlike ARfl, preferentially represses transcription d Expression of ARv7-repressed genes negatively correlates with recurrence d Re-expression of ARv7-repressed genes may serve as a biomarker of ARv7 inhibition

Progestin resistance is a major obstacle to treating early stage, well-differentiated endometrial cancer as well as recurrent endometrial cancer. The mechanism behind the suboptimal response to progestin is not well understood. The PTEN tumor suppressor gene is frequently mutated in type I endometrial cancers and this mutation results in hyperactivation of the PI3K/AKT pathway. We hypothesized that increased activation of AKT promotes an inadequate response to progestins in endometrial cancer cells. Ishikawa cells stably transfected with progesterone receptor B (PRB23 cells) were treated with the AKT inhibitor, MK-2206, which effectively decreased levels of p(Ser473)-AKT in a dose-dependent (10 nM to 1 uM) and time-dependent manner (0.5 h to 24 h). MK-2206 inhibited levels of p(Thr308)-AKT and a downstream target, p(Thr246)-PRAS40, but did not change levels of p(Thr202/Tyr204)ERK or p(Thr13/Tyr185)SAPK/JNK, demonstrating specificity of MK-2206 for AKT. Additionally, MK-2206 treatment of PRB23 cells resulted in a significant increase in levels of progesterone receptor B (PRB) protein. Microarray analysis of PRB23 cells identified PDK4 as the most highly upregulated gene among 70 upregulated genes in response to R5020. Inhibition of AKT further upregulated progestin-mediated expression of PDK4 but did not affect another progestin-responsive gene, SGK1. Treatment of PRB23 cells with R5020 and MK-2206 independently decreased viability of cells while the combination of R5020 and MK-2206 caused the greatest decrease in cell viability. Furthermore, mice with xenografted tumors treated with MK-2206 alone or with progesterone alone exhibited modest reductions in their tumor volume. The largest decrease in tumor size was observed in the mice treated with both MK-2206 and progesterone; these tumors exhibited the least proliferation (Ki67) and the most apoptosis (cleaved caspase-3) of all the treatment groups. In summary, inhibition of AKT stabilizes the Progesterone Receptor B and augments progesterone response in endometrial cancer cells that have hyperactivated AKT.

Progestins have long been used clinically for the treatment of endometrial cancers, however, the response rates to progestin therapy vary and the molecular mechanisms behind progestin insensitivity are poorly understood. We hypothesized that in PTEN mutated endometrial cancers, hyperactive Akt signaling downregulates Progesterone Receptor B (PRB) transcriptional activity, leading to overall impaired progestin responses. We report that inhibition of Akt with the Akt inhibitor, MK-2206 (MK), in conjunction with progestin (R5020) treatment, is sufficient to upregulate a subset of PRB target genes in Ishikawa cells stably expressing PRB (PRB-Ishikawa). Through gene ontology analysis of Akt-regulated PRB target genes, angiogenesis was found to be the principle process regulated by Akt-PRB. To further interrogate the mechanism by which Akt modulates PRB transcriptional activity, ChIP-Mass Spectrometry was performed to identify potential cofactors that differentially interact with PRB in the presence of the R5020 and MK+R5020. 14-3-3σ was identified as a protein enriched in the MK+R5020 dataset, and it was demonstrated that 14-3-3σ is required for the upregulation in PRB target gene expression following inhibition of Akt. In order to determine the ramifications of MK+R5020 treatment on angiogenesis, in vitro assays were performed and combinatorial MK+R5020 treatment significantly decreased endothelial cell invasion and tube formation more than MK or R5020 treatment alone. Furthermore, we found that combinatorial MK-2206+Progesterone treatments decreased angiogenesis and proliferation in the Ptend/d conditional mouse model of endometrial cancer. Taken together, these findings suggest that a combinatorial therapeutic approach utilizing Akt inhibitors with progestins may improve the efficacy of progestin therapy for the treatment of endometrial cancer.

Progesterone plays an essential role in the maintenance of the endometrium; it prepares the endometrium for pregnancy, promotes decidualization, and inhibits estrogen-dependent proliferation. Progesterone function is often dysregulated in endometrial disease states. In addition, the PI3K/AKT signaling pathway is often overactive in endometrial pathologies and promotes the survival and proliferation of the diseased cells. Understanding how AKT influences progesterone action is critical in improving hormone-based therapies in endometrial pathologies. Here, we summarize recent studies investigating the crosstalk between the AKT pathway and progesterone receptor function in endometriosis and endometrial cancer.

Androgens are important determinants of normal and malignant prostate growth. They function by binding to the C-terminal ligand-binding domain (LBD) of the androgen receptor (AR). All clinically approved AR-targeting antiandrogens for prostate cancer therapy function by competing with endogenous androgens. Despite initial robust responses to androgen deprivation therapy, nearly all patients with advanced prostate cancer relapse with lethal castration-resistant prostate cancer (CRPC). Progression to CRPC is associated with ongoing AR signaling, which in part, is due to the expression of constitutively active AR splice variants that contain the N-terminus of the receptor but lack the C-terminus. Currently, there are no approved therapies specifically targeting the AR N-terminus. Current pharmacologic targeting strategies for inhibiting the AR N-terminal region have proven difficult, due to its intrinsically unstructured nature and lack of enzymatic activity. An alternative approach is to target key molecules such as the cochaperone BAG1L that bind to and enhance the activity of the AR AF1. Here, we review recent literature that suggest Bag-1L is a promising target for AR-positive prostate cancer.

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Immunotherapies have yet to demonstrate significant efficacy in the treatment of hormone receptor positive (HR+) breast cancer. Given that endocrine therapy (ET) is the primary approach for treating HR+ breast cancer, we investigated the effects of ET on the tumor immune microenvironment (TME) in HR+ breast cancer. Spatial proteomics analysis of primary HR+ breast cancer samples obtained at baseline and after ET from patients enrolled in a neoadjuvant clinical trial (NCT02764541) indicated that ET upregulated B2-microglobulin and influenced the TME in a manner that promotes enhanced immunogenicity. To gain a deeper understanding of the underlying mechanisms, the intrinsic effects of ET on cancer cells were explored, which revealed that ET plays a crucial role in facilitating the chromatin binding of RelA, a key component of the NF-κB complex. Consequently, heightened NF-κB signaling enhanced the response to interferon-gamma, leading to the upregulation of β2-microglobulin and other antigen presentation-related genes. Further, modulation of NF-κB signaling using a SMAC-mimetic in conjunction with ET augmented T-cell migration and enhanced MHC-I specific T-cell mediated cytotoxicity. Remarkably, the combination of ET and SMAC-mimetics, which also block pro-survival effects of NF-κB signaling through the degradation of inhibitors of apoptosis (IAP) proteins, elicited tumor regression through cell-autonomous mechanisms, providing additional support for their combined use in HR+ breast cancer.

Ovarian cancer is the leading cause of death among gynecologic malignancies. Epidemiological evidence has suggested a role for steroid hormones in the pathogenesis of ovarian cancer, however, their precise role in ovarian cancer remains unknown. We hypothesized that Estrogen Receptor α (ERα) drives a transcriptional program that is sufficient to promote ovarian cancer cell proliferation in ER+ ovarian cancers. Preliminary data generated in our laboratory has suggested that estradiol (E2) treatment increases cell proliferation in PEO1 and OVKATE cells, ERα+ ovarian cancer cell lines. This increase in cell proliferation can be inhibited by co-administration with the selective estrogen receptor modulator, Tamoxifen, and the selective estrogen receptor degrader, Fulvestrant. To further interrogate the mechanism of action of ERα in ovarian cancer, we performed RNA-seq on PEO1 cells treated with Vehicle, 10 nM E2, 100 nM Fulvestrant, and E2+Fulvestrant for 4 and 24 hours. We identified 86 significantly differentially expressed genes following 4 hr E2 treatment and 659 significantly differentially expressed genes following 24 hr E2 treatment. Fulvestrant inhibited the majority of E2-induced differentially expressed genes, confirming that these genes are dependent upon ERα. Gene Set Enrichment Analysis (GSEA) indicated that the Hallmark early and late estrogen responses and G2/M checkpoint as positively enriched in our dataset, indicating that classical ER pathways are intact in these cells. To further characterize the transcriptional role of ERα in ovarian cancer cells, ChIP-seq was performed on PEO1 cells treated with Vehicle, E2, Tamoxifen, or E2+Tamoxifen for 45 minutes. E2 treatment robustly increased ER recruitment to its regulatory regions when compared to Vehicle or Tamoxifen alone. Motif analysis of these ERα binding sites demonstrated a significant enrichment in members of the AP-1 transcription factor family, but not in known ERα cofactors FOXA1 and GATA3. Furthermore, using GIGGLE analysis to identify similar ChIP-seq datasets to the PEO1 dataset, we identified FOSL1, FOSL2, JUND, JUN, and FOS as among the datasets with the highest similarity scores to the E2 PEO1 dataset. In order to identify potential combinatorial endocrine therapies for ovarian cancer, we performed a genome-wide CRISPR screen in the presence of Fulvestrant in PEO1 cells. Among the top positively selected genes in the presence of Fulvestrant was the AP-1 family member, FOSL2, indicating that loss of FOSL2 contributes to Fulvestrant resistance and further confirmed the role of AP-1 factors in estrogen function. We also identified genes that confer sensitivity to Fulvestrant treatment; the E2F, PI3K/mTOR, and steroid hormone biosynthesis pathways are enriched in the Fulvestrant sensitizer genes. Further analysis is currently underway to determine synergistic combinations with Fulvestrant for the treatment of ovarian cancer. Citation Format: Irene I. Lee, Myles Brown. Characterizing the dependence of AP-1 transcription factors on Estrogen Receptor Alpha transcriptional activity and Fulvestrant sensitivity in ovarian cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3435.